Parametric models may be generated by a computer for producing animated characters with user-adjustable facial expressions. To simulate the appearance of muscle movement in a character's face, one or more types of models may be implemented. For one model, a character's face may be represented with a collection of contour lines and vertices. Dependent upon the desired level of resolution, an extremely large number of vertices (e.g., tens of thousands, millions, etc.) may be included in the model. By adjusting the position of the vertices, various facial expressions may be represented on the character face. For some facial expressions, relatively few vertex position adjustments are needed while significant adjustments may needed to for representing other facial expressions.
In some implementations, each facial expression is attained from a linear combination of a selected set of facial expressions (referred to as blendshapes). By adjusting one or more parameters associated with the linear combination, a range of facial expressions can be created while utilizing relatively small amounts of computational resources. For each blendshape, a deformable surface that represents the animated character's face may be divided into distinct shapes with non-intersecting boundaries. As such, adjacent shapes that can represent muscular movements tend not to interfere since the shapes do not overlap, however, the range of producible facial expressions that may be limited.